Abstract:
LEDs are widely used in displays, automobiles, handsets, notebook backlighting, TV backlighting, and general lighting. The light-emitting films - InAlGaP for red LEDs, and InAlGaN for their blue and green cousins - need to be grown on a carrier substrate.

There is no good substrate to match the GaN material system, in terms of lattice constant and thermal expansion, but it is possible to grow high-quality films on sapphire, SiC and silicon.

Almost all GaN-based LEDs are fabricated on sapphire substrates, and Cree is the notable exception, using SiC substrates instead.

Massive adoption of solid-state lighting requires further advances in large-scale, low cost manufacturing. Siliconbased GaN LEDs have been attracting researchers in universities and industry for many years, due to their promise of large-scale production and compatibility with the IC manufacturing platform. In comparison, sapphire and SiC substrates are much smaller, and they can't be processed through silicon lines.